1. Field of the Invention
The present invention relates to a display device, and more particularly, to a liquid crystal display device having a backlight unit.
2. Background of the Related Art
Presently, display devices serve as very important visual information transfer mediums, and can be categorized into different types, such as luminescent types that include cathode ray tube (CRT) devices, electro-luminescent (EL) displays, light emitting diode (LED) devices, vacuum fluorescent display (VFD) devices, field emission display (FED) devices, and plasma display panel (PDP) devices, and non-luminescent types that require separate luminescent units to produce light, such as liquid crystal display (LCD) devices. The liquid crystal display (LCD) devices display images by making use of optical anisotropy of liquid crystals. In the LCD devices, the liquid crystals do not emit light, but receive, modulate, and transmit light onto a display panel. Accordingly, the liquid crystals require a light source, i.e., a backlight unit, to irradiate light onto a liquid crystal display panel.
FIG. 1 is a perspective assembly view of a liquid crystal display device according to the related art, and FIG. 2 is a perspective view of the liquid crystal display device of FIG. 1 according to the related art. In FIGS. 1 and 2, a liquid crystal display device consists of a liquid crystal display panel 10 for providing an image, a backlight unit 20 installed along a back of the liquid crystal display panel 10 to emit light along an entire front of the liquid crystal display panel 10, and a rectangular frame type metal chassis 30 supporting and affix each corner of the liquid crystal display panel 10 to the backlight unit 20. The liquid crystal display panel 10 includes an array substrate 11, a color filter substrate 12, liquid crystals (not shown) injected between the array and color filter substrates 11 and 12, and a driving circuit unit 13.
The backlight unit 20 functions to provide planar light having a uniform brightness from a fluorescent lamp 43. Accordingly, a thickness and power consumption of the liquid crystal display device is dependent upon how thin the profile of the backlight unit 20 is and how efficiently light is used. The backlight unit 20 includes a lamp assembly 45 having the fluorescent lamp 43 therein, a reflection sheet 21 that reflects light emitted from the fluorescent lamp 43 thereupon, a light guide plate 22 that guides the light, a plurality of optical sheets 23 installed on an upper surface of the light guide plate 22 to diffuse and condense the light transferred from the light guide plate 22, a mold frame 24 sequentially stacking to receive the reflection sheet 21, the light guide plate 22, the optical sheets 23, and the lamp assembly 45 therein, and a bottom cover 25.
The mold frame 24 is made of a plastic-based material and includes a reception space having a predetermined depth and a continuous step sill over a surface bent toward the reception space. The mold frame 24 encloses edges of the light guide plate 22 and lamp assembly 45 stacked within the reception space. In addition, the optical sheets 23 and the liquid crystal display panel 10 are sequentially received on the step sill over the surface of the mold frame 24, thereby providing overall support for the liquid crystal display device.
The lamp assembly 45 includes the fluorescent lamp 43, lamp holders (not shown) that are inserted in both ends of the fluorescent lamp 43, a lamp cover 44 enclosing an outer circumference of the fluorescent lamp 43 to improve light efficiency by reflecting the light emitted from the fluorescent lamp 43 toward the light guide plate 22, and wires (not shown) for transferring power to the fluorescent lamp 43.
The lamp cover 44 is made of a metal based material, and its inner surface is coated with silver (Ag) or covered with a silver (Ag) sheet to function as a reflector. The lamp cover 44 is made using a complex-processed expensive material, thereby increasing product costs of the liquid crystal display device. Furthermore, small impacts will deform the lamp cover 44, unless the lamp cover 44 is fully enclosed by the mold frame 24. However, this complicates assembly of the liquid crystal display device. In addition, light unnecessarily leaks out through a gap between the deformed portion of the lamp cover 44 and the optical sheets 23 or reflection sheet 21, thereby degrading image quality of the liquid crystal display device. Moreover, the gap increases as the device is subjected to additional impacts, thereby increasing the light leakage.
In order to prevent the light leakage, a black shield is formed along edges of the optical sheets 23, which corresponds to an end of a path of the light leakage, or a pad may be formed to extinguish the light. However, a method of forming the shield on an upper diffusion sheet (not shown) of the optical sheets 23 to prevent the light leakage complicates the sheet preparing process. In addition, a method of forming the pad complicates the assembly process of the liquid crystal display device and increases an overall thickness of the liquid crystal display device.